In:
Physiology, American Physiological Society, Vol. 38, No. S1 ( 2023-05)
Abstract:
Introduction: The myocardium is made up of many elements that each play an important role in heart function. The contractile cardiomyocytes proliferate prenatally, and become terminally differentiated in the weeks leading up to birth. Despite a loss of ~ 1/3 of the cardiomyocytes about 1 week before birth, the hearts continue to increase in size (Jonker et al., 2015). At birth, the demands on the cardiovascular system change, which may affect the relative cellular makeup of the myocardium. In this study, we determined the fractional composition of the myocardium in four different ages around the time of birth. Methods: Hearts, arrested in diastole, were collected from control fetal (135d and 142d gestational age; dGA; term is 147d) and newborn (1d and 5d postnatal age; PN) lambs. Sections of left ventricle were fixed (4% paraformaldehyde), paraffin embedded and stained (Masson’s Trichrome). Images (400x) were analyzed by unbiased sampling (grid system, FIJI) to classify according to these categories: cardiomyocyte cell body, cardiomyocyte nucleus, blood vessel lumen, blood vessel wall, collagen, non-collagen connective tissue. All values are represented as percent of total area (±SD). Groups (n=3-4 each age) were compared by 1-way ANOVA followed, if indicated, by Tukey's multiple comparisons test. Males and females were both represented in each age (135dGA, 143dGA, 1dPN, 5dPN: n=1/2, 2/2, 3/1, 2/1, respectively). Results: The average area composed of cardiomyocyte for all groups was 81.7 ± 7.4%, and did not differ between ages. The average area composed of vasculature for all groups was 8.6 ± 5.2%, and did not change with age. Connective tissue area was 3-fold greater at 1dPN (8.5 ± 3.6%) than 143dGA (2.8 ± 1.2%, P 〈 0.05) and 5dPN (2.5 ± 0.8%, P 〈 0.05). This was not due to more collagen, which did not differ between ages. Further analysis of the cardiomyocyte fraction indicated that the nucleus was 60% larger (compared to total myocyte area) at 1dPN (P 〈 0.04; in advancing age order: 18.2 ± 3.3%, 14.2 ± 1.0%, 26.3 ± 4.9%, 17.1 ± 1.8%). Conclusion: Our preliminary analysis indicates little change in the cellular composition of the left ventricle myocardium, save for a transient increase in connective tissue area and larger nuclei per cardiomyocyte area 1 day after birth. A change in glycogen after birth could be a factor that leads to increased cardiomyocyte nuclear area per cytoplasm and increased relative fraction of connective tissue. This study was funded by NIH NHLBI R01HL142483. KAVR was funded by a NIH supplement to R01HL142483. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.
Type of Medium:
Online Resource
ISSN:
1548-9213
,
1548-9221
DOI:
10.1152/physiol.2023.38.S1.5735062
Language:
English
Publisher:
American Physiological Society
Publication Date:
2023
detail.hit.zdb_id:
3115360-4
detail.hit.zdb_id:
2005759-3
SSG:
12
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